1. Field of the Invention
The present invention relates to a scroll-type capable of, for example, being used in a refrigerating circuit in an air conditioning system for an automobile.
2. Description of Related Art
Known in the prior art is a scroll-type compressor which includes a fixed scroll member, a movable scroll member which is arranged to face the fixed scroll member, a rotating shaft and a bushing member which is located on an end of the shaft in such a manner that, with respect to the shaft, the bushing is eccentric, on which bushing the movable scroll member is relatively rotatably supported. A rotating movement of the drive shaft causes the movable scroll member to effect an orbital movement, while the movable scroll member is prevented from being rotated about its own axis, so that, between a scroll wall of the fixed scroll member and a scroll wall of the movable scroll member, closed chambers are formed, the volume of which varies in accordance with the orbital movement of the movable scroll member. During the orbital movement of the movable scroll member, the closed chambers are moved radially inwardly toward the inner ends of the fixed and movable scroll members, so that a refrigerant gas in the closed chambers is discharged from an outlet port formed in a scroll base plate of the fixed scroll member.
During the compression operation, the scroll walls of the fixed and movable scroll members are brought into contact with each other at a plurality of spaced locations. Thus, any inaccuracy in the shape of the fixed and movable scroll members at these location from the desired shape causes the medium to leak, thereby reducing the compression efficiency. Thus, some means is necessary to compensate the above mentioned inaccuracy in the shape of the scroll members, thereby maintaining the desired contacted condition between the scroll portions of the fixed and movable scroll members.
Thus, in the Japanese Unexamined Patent Publication (Kokai) No. 2-176179, a construction is proposed wherein the scroll compressor has a drive shaft having, at its one end, drive projections defining driving force transmission surfaces, and a bushing having grooves defining driving force receiving surfaces. These drive projections and grooves are engaged with each other in such a manner that the driving force transmission surfaces and driving force receiving surfaces are slidably movable with each other. Furthermore, the planes on the driving projections are, with respect to a line passing through the axis of the bushing and of the rotating shaft, inclined rearwardly in the direction of the rotation of the rotating shaft.
Thus, when the bushing receives a compression reaction force from the movable scroll member, the bushing moves along the planes on the driving projections, so that the radius of the orbital movement of the movable scroll during the operating (rotating) condition of the compressor becomes larger than that during the non-operating (stopping) condition of the compressor. In other words, during the orbital movement of the movable scroll member, a compression reaction force acts on the bushing in order to obtain an increased radius of the orbital movement, thereby maintaining the scroll wall members in contact with each other, irrespective of an existence of small inaccuracies in the scroll profiles of the members.
In the operation of the compressor of the above mentioned Japanese Unexamined Patent Publication No. 2-176179, a small radius of the orbital movement of the movable scroll member is obtained until the compression reaction force is increased after the commencement of the operation of the compressor. The small value of the radius of the orbital movement of the movable scroll member allows a space to be created between the scroll walls of the fixed and movable scroll members irrespective of a fact that the compressor is operated. Such a generation of the space can, which is continued for a suitable period, reduce the rapidity of the increase in the load when the compressor is brought into the operation, thereby reducing vibration as well as shock otherwise generated when the compressor is switched on.
In a scroll type compressor, a balance weight is usually provided for canceling the centrifugal force generated by the movable scroll member which is subjected to an orbital movement. However, it is difficult to provide a balance weight of a desired value which is effective to fully balance the centrifugal force due to the fact that an available space is limited. As a result, a residual centrifugal force, which is out of the balancing range of the balancing weight, causes the radius of the orbital movement to be rapidly increased after the compressor is switched on, and an effective suppression of a rapid increase in the load upon the switching on the compressor cannot be obtained.
Furthermore, the prior art compressor suffers, also, from a problem in that the compressor tries to compress the liquid refrigerant when the compressor is brought into an operation after a prolonged period of the stoppage due to the fact the refrigerant is liquidized during such a prolonged stoppage. The above mentioned residual centrifugal force causes the radius of the orbital movement to be rapidly increased after the switching on of the compressor, causing the clearance between the scroll walls to be rapidly reduced. As a result, a compression of a liquid state refrigerant is rapidly generated, thereby producing an abnormally increased pressure, thereby producing noise, damage to the scroll walls and a delivery valve, as well as slippage at the frictional surfaces of an electromagnetic clutch.